linux-kernel - Re: [PATCH -mm] splice: Disable vmsplice on nommu.

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Message-ID: <20070911112526.GK15405@kernel.dk>
Date:	Tue, 11 Sep 2007 13:25:27 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Ungerer <gerg@...pgear.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] splice: Disable vmsplice on nommu.

On Tue, Sep 11 2007, David Howells wrote:
> Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> > It's a bit of a sledge hammer... Since get_user_pages() appears to work
> > on nummu, we can just disable the vmsplice-to-userspace bits and leave
> > the (working) vmsplice-from-userspace in place.
> 
> That sounds about right.  I don't think you can do the latter without
> an MMU, but I may be wrong about what it does.

You mean the former? The latter is vmsplice() filling a pipe with user
pages, using get_user_pages() to set them up. And that looks like it
should work on nommu.

The former is vmsplice() using mmap like functionality to map pages into
a user vma.

Just making sure we agree :-)

-- 
Jens Axboe

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